Bulb filament



FIG. 1 is a front view of a bulb filament showing our new design, with the back view being a mirror image thereof;

FIG. 2 is a side view of the bulb filament shown in FIG. 1, with the other side view being a mirror image;

FIG. 3 is a top view of the bulb filament shown in FIG. 1; and,

FIG. 4 is a bottom view of the bulb filament shown in FIG. 1.

The broken lines depicting the glass bulb, base, and portions of the stem show unclaimed subject matter for the design. 

CLAIM The ornamental design for a bulb filament, as shown and described. 